Thermostat location on '02 GMC 5.3L

I'v noticed that my incoming heat has not been as warm so checked the temp gauge and it read low. This probably indicates the need for a thermostat replacement. I checked the hose from the radiator to the block and I don't see where the thermastat is located. Any direction as to it's location would be helpful.
Thanks
Jim

Thanks for the info dipstick. Much appreciated. I have always had Ford trucks before getting my 2002 GMC and the t-stat housing was always on top of the block, so this one threw me for a loop. I would not trade my GMC for a Ford anymore. Thanks again.
Jim